Halliday & Matthiessen (2014: 138):
What is more significant, however, is that the whole concept of exchanging information is difficult for a young child to grasp. Goods–&–services are obvious enough: I want you to take what I am holding out, or to go on carrying me, or to pick up what I have just dropped; and although I may use language as a means of getting what I want, the requirement itself is not a linguistic commodity — it is something that arises independently of language. Information, on the other hand, does not; it has no existence except in the form of language. In statements and questions, language itself is the commodity that is being exchanged; and it is by no means simple for a child to internalise the principle that language is used for the purpose of exchanging language. He has no experience of ‘information’ except its manifestation in words.